The multi-faceted functions of skin are conferred by its unique three dimensional architecture made up of multiple modules interwoven into an integral organ. To function normally, the size, number, ratio and relative positions of each component have to be precisely regulated. Few studies have focused on how the complex pattern of the skin is built. Current management of severe skin injury has achieved the goal of saving patients' lives by growing a flat layer of epidermis and dermis over the wound. Life-saving as it may be, the replaced skin is composed of relatively simple flat epidermis and dermis and does not function in full due to the lack of skin appendages and key functional modules. Toward the long term objectives of regenerative medicine, we aspire to learn fundamental principles of skin organogenesis that we can apply to better wound healing/regeneration and tissue engineering. In the previous funding period, we focused on the morphogenesis of a single appendage. We now want to study the multi-faceted skin as a whole and to reveal the unifying framework of skin morphogenesis at multiple spatio-temporal scales. We propose to study how the key functional modules of skin are built and patterned. Based on our preliminary data, we postulate that the construction of skin structures occurs through a series of tissue interactions, each with distinct patterning behaviors, built layer by layer, module by module, leading to the integration of the skin as a whole. We choose to focus on three components critical to avian skin function: the feathers, muscles that connect feathers for functionality, and pigment that decorates feathers for communication. Each component represents a different category of patterning behavior in a hierarchical framework. We will study how the boundary between appendage primordia and surrounding dermis is consolidated and hypothesize that periodic patterning, the most fundamental process of skin organogenesis, is established via competition and stabilization of cell adhesion / motility. We will study how the dermal muscle network is established and hypothesize that this adaptive patterning is achieved using appendage primordia as anchor points. We will analyze how the final patterns are pleomorphic and how the process is modulated by environment factors. We will study how skin pigment patterns are painted by the regulatory patterning process. We hypothesize that it is achieved through combinatorial regulation of the migration, proliferation, survival, and / or differentiation of melanocyte progenitors. Similar principles may be used in the patterning of other tissue components. Understanding these patterning behaviors will allow us to apply the principles and initiate self-organizing regenerative processes in various skin disease conditions. PUBLIC HEALTH RELEVANCE: Here we study the patterning mechanisms involved in the development of the skin organ. They include periodic patterning to set up periodically arranged appendage primordia, adaptive patterning to add more components onto extant architecture and regulatory patterning to modulate cell migration or differentiation under physiological or pathological conditions. The study should provide new insights into how the different components are integrated to build a complex organ, and will be useful toward the tissue engineering of a fully functional skin.